Scanning type photographic film developing system and apparatus

ABSTRACT

A system and apparatus is provided for developing photographic film such as X-ray film, for example, in a dental office, or in any other establishment. The system is capable of causing the film to be developed with any desired density, and within known limitations, regardless of whether the film has been over-exposed or under-exposed, and regardless of the temperature of the developing bath, and the age of the developing solution. The apparatus incorporates a control system which responds to the scanning of the exposed film in a developing solution by a radiant energy beam to which the particular film is relatively insensitive, and which causes the developing process to be terminated when a desired density is achieved. The system of the invention has a feature in that the very clear and very opaque areas, and other areas of no interest, are eliminated from the processing, and the desired density is established by processing the film between such minimums and maximums.

United States Patent [1 1 Gregg et a1. Q

[ SCANNING TYPE PHOTOGRAPHIC FILM DEVELOPING SYSTEM AND APPARATUS [75] Inventors: David P. Gregg, 1936 Kelton Ave.,

Los Angeles; Charles K. Pooley, Santa Monica, both of Calif.

[73] Assignee: said Gregg, by said Pooley [22] Filed: Jan. 19, 1973 [21] Appl. No.: 325,201

Related U.S. ApplicationData [63] Continuation of Ser. No. 214,924, Jan. 3, 1972 abandoned.

[52] U.S. CI. 95/89 R, 95/96 [51'] Int. Cl. .L G03d 3/10 [58] Field of Search 95/89 R, 96, 97,

[56] References Cited UNITED STATES PATENTS 1,959,233 5/1934 Franke.; 95/89 R 2,296,048 9/1942 Planskoy.... 95/89 R 3,388,652 6/1968 Parrent 95/89 R 3,554,109 l/l97l Street et a1 95/89 R 1?. P051) 20 foam- Mecan/c'd/ .Scawre/ [451 Jan. 15, 1974 Primary Examiner-Fred L. Braun Attorney-Keith D. Beecher [57] ABSTRACT A system and apparatus is provided for developing photographic film such as X-ray film, forexample, in a dental office, or in any other establishment. The systern is capable of causing the film to be developed with any desired density, and within known limitations, regardless of whether the film has been overexposed or under-exposed, and regardless of the temperature of the developing bath, and the age of the developing solution. The apparatus incorporates a control system which responds to the scanning of the exposed film in a developing solution by a radiant energy beam to which the particular film is relatively insensitive, and which causes the developing process to be terminated when a desired density is achieved. The

- system of the invention has a feature in that the very clear and very opaque areas, and other areas of no interest, are eliminated from the processing, and the desired density is established by processing the film between such minimums and maximums.

6 Claims, 4 Drawing Figures 722 Van; 9r COILL/G/ Vac/14,100

PATENTEDJAN 15 1924 SHEEI 2 Bf 3 PATENTED JAN 1 51974 SHEET 3 BF 3 1. scANNlNc TYPE PHOTOGRAPHIC FILM DEVELOPING SYSTEM'AND APPARATUS This application is a continuation of copending application Ser. No. 214,924 filed Jan. 3, I972, and now abandoned, in the names of the present inventors.

BACKGROUND OF THE INVENTION example, from any appropriate radiant energy source to which the film is relatively insensitive; by subsequently transforming the energy in the beam passed through the film, and through the developer solution,

into electrical signals; andby processing the electrical signals, as will:be described.,At present, light energy towards the redendof the visual spectrum has been found to be appropriate for the beam.

As pointed out'in the copending application Ser. No. 141,538, a major problem in developing'photographic film is the establishment of that developing time, which will permit a'satisfactory density to be achieved, even though the film may have been over-exposed or underexposed, even though the temperature of the developing solution may vary, or even when the age of the developing solution is unknown. This problem of proper density in X-ray films is especially prevalent in. hospitals, clinics and dental offices, and it results in the technicians anddoctors either having to be satisfied with less than satisfactory density in the developed X-ray film, or his having to perform expensive and timeconsuming retakes.

The system and apparatus described in the copending application Ser; No. 141,538 at presentutilizes a red light beam as a basis forpcontr'olling the time in which the exposed X-ray film is actually submerged in the developing solution. Since the X-ray film is relatively insensitive'to red light energy, there is little tendency for it to be fogged by the beam. Also, by pulsing the source, excessive heating of the source may be avoided.

The system of the present invention, as explained above, likewise uses an appropriate energy beam to which the film is relatively insensitive for controlling the time in which theX-ray film is actually to be submerged in the developing solution. As also explained, in the system of the present invention,- the beam is scanned across the film, by any appropriate means, and the beam is subsequently detected and transformed into electrical signals, which are processed so that the appropriate control effects may be provided.

Therefore, in the practice of the present invention, an appropriate beam to which the film is relatively insensitive, which may be continuous or pulsed, is passed through the bath and developing solution and scanned across the filmbeing developed within the bath. The bath is detected after it has passed through the developing solution and through the film, so that electrical signals may be produced whose amplitude corresponds to the local attenuation of the detected beam. When the film has been developed to a predetermined density, the amplitudes of the electrical signals reach a certain value. The electrical signals are used to provide a desired control effect, as will be described.

In the apparatus of the copending application Ser. No. 141,538, reflectors are used for directing the energy, so that it may be passed through the solution in the form of a beam whose cross-section approximates the area of the film being processed. In that case, the energy in the beam is averagedover the entire area of thefilm being developed, and local variations in the film density, such as are caused by'tooth fillings, surgical clamps, and the like, have relatively little effect on the overall intensity of the beam. Under such conditions, the beam detected on the other side of the film has an amplitude determined by the overall contrast of the image being developed, as is desired.

In the system of the present inventiomon the other hand, the beam has a small cross-section, and it is scanned across the film, and across the portions of the ,solution forming a margin around the film. The variations in the resulting electrical signals due to the' aforesaid local variations which represent excessively opaque and transparent areas, are removed in the processing of the electrical signals, as are the variations in the electrical signals due-to highly transparent areas, such as the areas of the developing solution around the margin of the film, as well as areas representing flesh. Specific ally, the system is capable of detecting the presence of human flesh and of rejecting all other objects and transparentareas.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view, partly in block form, and somewhat schematically representing an appropriate system and apparatus for practicing the invention in one of its embodiments;

FIG. 2 is an electrical circuit diagram, partly in block form, showing the electrical processing system associated with the apparatus of FIG. 1; and

FIGS. 3 and 4 are curves useful in understanding the operation of the system of the invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT As shown in FIG. 1, the apparatus includes a transparent bath or tank 10 in which an appropriate developing solution is contained. An exposed photographic or X ray film 12 is suspended in the solution in the tank 10 by a suitable film hanger 14. The film hanger 14, for example, may be part of an automatic film processing apparatus, whereby the film is carried from one bath to another during the developing process. An energy source 16 is provided. This source, for example, may be a red light emitting diode, a red laser, or any other appropriate type of energy source. The source may be pulsed, for example, at a rate of I000 times a second by a suitable pulsing circuit represented by the block 18, to prevent excessive heating. The pulse width may, for example, be of the order of 200 nanoseconds, although any appropriate parameters may be used. The source 16 is moved by any appropriate mechanical scanner indicated by the block 20, or the film itself is moved, or both, so as to cause the beam from the source to be scanned across the tank 10 and across the film 12 within the tank. The scanning occurs, for example, in a series of repeated lines spaced slightly from one another until the entire film area is covered. The

resulting scanning tasters are repeated throughout the developing of the film.

The scanned beam, after it has passed through the transparent tank 10, through the solution in the tank 10, and through the film 12, is detected by an energy detector and electrical transducer 30. The scanning beam may be reflected to the detector from all its scanning positions by means, for example, of a reflector 32 of an ellipsoidal, or other suitable shape. The apparent source of the beam is always at one focus point of the imaginary whole ellipsoid and the detector is always at the other focus point. The reflector 32 is positioned onv the opposite side of the tank from the scanning source 16. The detector 30, for example, may be a silicon photo diode, or any other appropriate sensor may be used.

The electrical output from the energy detector 30 is applied to an electrical processing circuit designated 34 and which is described in detail in FIG. 2. The output from the processing circuit 34 may be used, for example, to activate any appropriate indicator when a desired density has been achieved during the developing process of the X-ray film; or to operate an associated mechanism to cause the film 12 to be withdrawn from the tank 10 automatically at that time.

The electronic processing circuit 34 of FIG. 2 includes, for example, an amplifier A, which receives the electrical video signal from the IR detector 30. The amplifier output is connected to a delay line DL,, and also to a pair of diodes D, and D The diodes D, and D are connected in circuit with further diodes D and D at the output of the delay line DL,, and with a pair of resistors R, and R as shown. The resistor R, is connected to a positive potential source, and the resistor R is connected to a negative potential source.

The diode circuit is connected to a pair of differential comparators M, and M the comparators each having a second input terminal, one of which is connected through a diode D to a source V,, and the other being connected through a diode D to a source V The second input terminals of the comparators are interconnected by a resistor R The outputs of the differential comparators M,, and M control respective electronic switches designated SW, and SW The switch SW, switches a point a in the aforesaid diode circuit to a diode D and the switch SW switches a point b in the diode circuit to a diode D,,. The diode D is connected at a point c to a grounded capacitor C,, and to a low pass filter F,; and the diode D, is connected at a point d to a grounded capacitor C and to a low pass filter F The filters are also connected to ground.

The output of the low pass filter F, is connected to a unity gain amplifier A the output of which is connected by means of R to the positive input of the comparator M,,. The low pass filter F, is connected to the negative input of comparator M,,, the output of which controls switch SW,,. The output signal at SW, is applied to the input of SW,,, and, through R,,, to the positive input of comparator M,. A resistor R, is connected from the positive input of M,, to a negative potential source. The output of SW, is connected to a diode D,,, and capacitor C in a manner like SW, and SW the output e is connected to a low pass filter F which is in turn connected to the unity gain amplifier A whose output is connected by R, to the positive input of M,,.

The output h of comparator M is connected to an and gate G, and to one terminal of a rotary switch SW,. The output of G, is connected to a second terminal of the switch SW,. The output g of the comparator M, is connected to gate G, and to a third terminal of SW,,. The output dv/dt of the differentiator M is connected to an or" gate G and the movable arm of the switch SW, is also connected to the gate G,,. The output from the processing circuit 34 appears at an output terminal 50 which is connected to the output of the gate G The processing circuit 34 of FIG. 2 converts the output of the amplifier A, into two signals, one undelayed and the other delayed in the delay line DL, by a small fraction of a single scan across the film 12. Then, during each scan, the lesser of the two signals from the amplifier A, (delayed or undelayed) at any given moment appears at the junction 1 between the diodes D, and D and the greater of the two signals (delayed or undelayed) at the same moment during each scan appears at the junction 2 of the diodes D and D,.

The comparator M, changes its output to render the switch SW, conductive when its input 2" is less than the voltage V,. The voltage V, corresponds, for example, to a density of 0.5, or about 32 percent of the maximum transparency brightness that the film negative can achieve. Therefore, whenever the transparency exceeds the 32 percent level, the switch SW, is switched off, and such values do not affect the measurement of the film density. When the signal 2" appliedto the comparator M, is less than the voltage V however, the switch SW, is rendered conductive by the comparator M,, so as to pass the lesser of the two signals appearing at the point 1." This lesser signal is passed through the diode D to charge the capacitor C, positively. The capacitor C, is connected as a peak detector, and it follows the peak amplitude of the signal 1, as the scan continues. At the end of each scan, the charge on the capacitor C, holds, and it corresponds to the peak amplitude of the signal 1 during the preceding scan.

At the same time, the comparator M changes its output to render the switch SW conductive whenever the lesser of the two signals at point 1 is greater than the voltage V The voltage V is selected to represent a voltage corresponding, for example, to 0.1 percent of the maximum transparency value, or a density of 3.0. Therefore, any object which is encountered which makes the lesser voltage crop below the 0.1 percent value, during any scan, causes the switch SW to be turned off, so that the density of that object is not included in the measurement of the average contrast. However, as long as the signal at point 1 is greater than the 0.1 percent level, as represented as V the switch SW is rendered conductive by the comparator M and passes the greater signal at the point 2" through the diode D to charge the capacitor C negatively with respect to ground. The capacitor C, also is connected as a peak detector, and it measures the negative peaks of the signal at the point 2" during each scan.

Therefore, at the end of each scan, the charge across the capacitor C, is .a positive value with respect to ground, and appears at a point 3 as representative of the lightest value of the scanned line, whereas the negative voltage developed across the capacitor C2 at the end of each scan represents the darkest value encountered during the scan, the latter signal appearing at the point 4." The signals at the points 3" and 4 are filtered by the respective filters F, and F which, as indicated, are low pass filters. The resulting signals at the outputs of the low pass filters F, and F have a long time constant as compared with the scanning frame rate, so that maximum and minimum brightness over the entire film area is represented by such signals, with spurious changes due to opaque objects or excessive transparent areas being removed.

The negative-going, or maximum density signals are furthermore switched by SW by the output of M The inputs to M, are the maximum density determined as described above, and appearing at F,, and the instantaneous result of SW with a small fixed bias applied by R and R in such a way that the two inputs of M are at the same potential when the signal from SW is, say, a factor of 2 lighter, or showing a density of 0.3 less, than the maximum density value held at C (signal d).

The sw itch SW then switches on only when the value is 0.3 or more less dense than the peak density, this being then rectified by D,, and stored in capacitor C, as

signal e. This signal represents the darkest area which is at least 0.3 less dense than the densest portions of the I image. For example, the background air surrounding an X-rayed subject, the darkest part of the film, is rejected from further processing.

With reference to FIG. 3, for example, scanning values are represented thereby as the developing process continues. For example, for each scan, a maximum brightness occurs at the part a of the curve as the beam passes through the solution surrounding the film negative. Then, a maximum dark line appears as the curve drops to b, as the beam encounters a bracket or support, or other opaque object. The beam then rises to a peak again as it moves to the margin of the film, the latter peak being designated a. Then, early in the scanning process, and while the film is still coated with the opaque coating which is usual for such films, the scanning beam drops in intensity to the level represented as c, and this continues for each scanning line until the margin of the film is reached, and the beam again rises to the maximum brightness level, as represented by a", as -it again encounters the transparent solution.

It will be appreciated that for the initial part of the developing process, the effect of the beam is to con tinue to produce output signals corresponding in amplitude to the curve 0, until the opaque coating is dis solved. Then, the film negative is revealed in its undeveloped and highly transparent state, so that the scanning beams exhibit a brightness for each scan as represented by the dotted curve d. This condition continues until the development starts, and the film negative begins to darken. Then the resultant of the scans drops to the level represented, for example, by e. As the developing process continues, the detected beam intensity then further drops to the values represented by f. If the developing process is continued too long, the whole film negative-blackens, and the. resultant intensity of the detected scanning beam drops to the value shown, for example, as g.

The circuit of FIG. 2, as thus far described, follows the curves d, e, f, and g, for example but rejects the peaks a, b, a, a" and c, as being either less dense than 0.5, or more dense than 3.0 and subsequently rejecting those portions of the signal which pass the first criterion but which lie within, for example, 0.3 of the darkest portion, the limit being 3', andf for e andfin FIG. 3. The outputs from the filters F, and F, as the develop ing process progresses, are represented by the curve of FIG. 4. For example, at the beginning of the developing process, during which any opaque coating which might or might not be present has not been dissolved from the film negative, the resulting dark signal results in corresponding signals from the filters F, and F As any such coating is dissolved, the effect of the transparency rises to the peak A, and both the filters F, and F during this interval, generate essentially the same amplitude signals, since no density has as yet been established. However, as the developing process progresses still further, and as the images are developed on the film negative, the two signals from the filters F, and F decrease. However, the signal from the filter F,, as represented by the curve C is of greater amplitude than the signal from the filter F as represented by the curve B. Therefore, on the negative slope of the curves B and C, the difference in amplitude at any time, such as the time T, between the two curves represents the contrast. As the developing process is further continued, both curves drop to the minimum value, as the film becomes completely darkened. Y

' The circuit of FIG. 2 may be adjusted in different ways to stop the developing process for different criteria. For example, if the switch SW, is set to terminal I, the output of the differential comparator M is used to produce the output signal at the output terminal 50, and this occurs when the darkest portion of the picture area being evaluated reaches a predetermined level, as determined by the setting of a potentiometer 60. The differentiator M assures that an output will be developed only in the presence of the increasing darkness,

or increasing density,-so as to prevent spurious outputs during the initial part of the developing process, and when the curve of FIG. 4, for example, is rising, rather than falling. This is implemented by applying the output of the differentiator M to the or gate G so that the or gate is enabled to permit an output to be produced, only at times of decreasing output from the filtr F2.

When the switch SW, is set tothe terminal 3, the output of the differential comparator M, is used to develop the output at the terminal 50. In the latter case, the outputs from filters F, and F,, are, with the aid of unity gain amplifiers A and A averaged by R and R so that the potential of the input of M represents a density intermediate between the lightest and darkest areas being processed. By means of potentiometer 61, the level at which M, changes its output is adjusted to signal when the above determined average density reaches the point where development should stop.

When the developing switch SW. is set to the number 2 contact, the output from the comparator M, is checked against an arbitrary value from the comparator M so that the developing process can be stopped when the output from either of the comparators M or M, becomes zero.

As explained above, many X-ray films are coated with an opaque coating which dissolves in the developer, and which should not be confused with video information. The differentiator M as explained, develops a negative output when the slope of the dark curve (B in FIG. 4) is negative, indicating that the opaque coating has been dissolved, and the information is actually video information. nly during the latter condition is the stop command signal passed through the gate G to the output terminal 50. On the other hand, when the opaque coating is being dissolved, the darkness curve of FIG. 4 has a positive slope A, and the gate G is disabled at this time, so as to prevent spurious outputs.

While the description is concerned with a linear type of X-ray negative whose transmittance is inversely proportional to the exposure, that is, the density is equal to the log of the exposure, which assumes the gamma to be 1, the system can operate with films and developers giving a gamma other than 1, whether by making the log amplifier A adjustable, or making suitable allowances in the settings of potentiometers 60 and 61.

Also, other combinations of indicators than the above illustrated average and maximum density of the selected picture can easily be used. For example, by filtering without peak deflection, the signals from SW and SW can be the RMS values of the lighter and darker densities, or some or all the signals could be passed through band pass filters and treated as AC signals, and finally be rectified and detected.

The invention provides, therefore, an automatic X-ray film developing system which permits a true optimum density, or any other percentage of contrast ratio, to be attained without the concomitant need for accurate control of the development bath temperature or of the developer solution. The system of the invention is advantageous in that it operates accurately with all sizes of X-ray film, since the light transmission through the marginal solution is not used in the determination of the contrast by the system. Moreover, the system also rejects any signals generated due to the presence of X-ray opaque materials, such as metallic prosthetics, dental fillings, and the like, and also background areas of air which surround many X-ray subjects, all of which otherwise would have a spurious effect on the determination of the desired image density. In addition, the system of the invention automatically compensates for underor over-exposure of the X-ray film, as well as for variation in the sensitivity of the X-ray film from source-to-source and from lot-to-lot.

The foregoing features of the invention are accomplished by eliminating the time-of-development as the controlling factor of the developing process, and by substituting a continuous optical evaluation of the development quality as the developing process proceeds.

This basic premise, together with the scanning technique, and associated electronics, enables the features of the invention to be achieved. It is evident that although a particular embodiment of the invention has been shown as described, modifications may be made. It is intended in the following claims to cover all modifications which fall within the spirit and scope of the invention.

What is claimed is: v

'1. Photographic film developing apparatus and system including: a tank for a film developing solution; a source of radiant energy to which the film is relatively insensitive positioned to direct a beam of said energy through said solution in said tank; means for supporting a film to be developed in said tank in the path of said beam; scanning means coupled to said source for scanning said beam across said film; an energy detector positioned to receive the beam after it has passed through said flim for producing an electric signal representative of the intensity of said beam as received by said detector; and electrical circuit means coupled to said detector for developing an output indicative of when the density of the image developed on the film reaches a predetermined value, said circuitry including an input circuit coupled to said detector for developing a first signal which increases in amplitude as the brightness of the beam received by the detector increases from a reference level, and for developing a second signal which increases with amplitude as the brightness of the beam received by the detector decreases from a reference level, a first channel coupled to said input circuit for processing said first signal and including first peak detector means for producing a first output corresponding to the peak amplitude of the first signal, a second channel coupled to said input circuit for processing said second signal and including second peak detector means for producing a second output corresponding to the peak amplitude of the second signal; and an output circuit coupled to said first and second channels for developing the aforesaid output indicative of when the density of the image, or any portion of the image, developed on the film reaches a predetermined value.

2. The apparatus and system defined in claim 1, and which includes first switching means included in said first channel for de-activating said first channel when the amplitude of said first signal exceeds a predetermined threshold, and second switching means included in said second channel for de-activating said second channel when the amplitude of said second signal exceeds a predetermined threshold.

3. The apparatus and system defined in claim 1, in which said output circuit includes differential comparator means connected to said first and second channels for causing said output circuit to develop its output when the differential between said first and second signals reaches a predetermined level.

4. The apparatus and system defined in claim 1, in

which said output circuit includes differential comparator' means connected to said second channel for causing said output circuit to develop said output when said second signal reaches a predetermined level.

5. The apparatus and system defined in claim 1, in which said output circuit includes differential comparator means connected to said first channel for causing said output circuit to develop-said output when said first signal reaches zero amplitude.

6. The apparatus and system defined in claim 1, in which said output circuit includes differentiator means connected to one of said channels, and a gate circuit connected thereto, for preventing said output circuit from developing an output except during intervals when said first and second signals are decreasing in amplitude with time. 

1. Photographic film developing apparatus and system including: a tank for a film developing solution; a source of radiant energy to which the film is relatively insensitive positioned to direct a beam of said energy through said solution in said tank; means for supporting a film to be developed in said tank in the path of said beam; scanning means coupled to said source for scanning said beam across said film; an energy detector positioned to receive the beam after it has passed through said flim for producing an electric signal representative of the intensity of said beam as received by said detector; and electrical circuit means coupled to said detector for developing an output indicative of when the density of the image developed on the film reaches a predetermined value, said circuitry including an input circuit coupled to said detector for developing a first signal which increases in amplitude as the brightness of the beam received by the detector increases from a reference level, and for developing a second signal which increases with amplitude as the brightness of the beam received by the detector decreaseS from a reference level, a first channel coupled to said input circuit for processing said first signal and including first peak detector means for producing a first output corresponding to the peak amplitude of the first signal, a second channel coupled to said input circuit for processing said second signal and including second peak detector means for producing a second output corresponding to the peak amplitude of the second signal; and an output circuit coupled to said first and second channels for developing the aforesaid output indicative of when the density of the image, or any portion of the image, developed on the film reaches a predetermined value.
 2. The apparatus and system defined in claim 1, and which includes first switching means included in said first channel for de-activating said first channel when the amplitude of said first signal exceeds a predetermined threshold, and second switching means included in said second channel for de-activating said second channel when the amplitude of said second signal exceeds a predetermined threshold.
 3. The apparatus and system defined in claim 1, in which said output circuit includes differential comparator means connected to said first and second channels for causing said output circuit to develop its output when the differential between said first and second signals reaches a predetermined level.
 4. The apparatus and system defined in claim 1, in which said output circuit includes differential comparator means connected to said second channel for causing said output circuit to develop said output when said second signal reaches a predetermined level.
 5. The apparatus and system defined in claim 1, in which said output circuit includes differential comparator means connected to said first channel for causing said output circuit to develop said output when said first signal reaches zero amplitude.
 6. The apparatus and system defined in claim 1, in which said output circuit includes differentiator means connected to one of said channels, and a gate circuit connected thereto, for preventing said output circuit from developing an output except during intervals when said first and second signals are decreasing in amplitude with time. 